Beneath the hoods of millions of the clean electric cars rolling onto the world’s roads in the next few years will be a dirty battery.

Every major carmaker has plans for electric vehicles to cut greenhouse gas emissions, yet their manufacturers are, by and large, making lithium-ion batteries in places with some of the most polluting grids in the world.

By 2021, capacity will exist to build batteries for more than 10 million cars running on 60 kilowatt-hour packs, according to data of Bloomberg NEF. Most supply will come from places like China, Thailand, Germany and Poland that rely on non-renewable sources like coal for electricity.

“We’re facing a bow wave of additional CO2 emissions,” said Andreas Radics, a managing partner at Munich-based automotive consultancy Berylls Strategy Advisors, which argues that for now, drivers in Germany or Poland may still be better off with an efficient diesel engine.

The findings, among the more bearish ones around, show that while electric cars are emission-free on the road, they still discharge a lot of the carbon-dioxide that conventional cars do.